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A balanced diet must contain carbohydrate,
protein, fat, vitamins, mineral salts and fibre. It must contain these things in the
correct proportions.
Index
Carbohydrates: these provide a source of energy.
Proteins: these provide a source of materials for growth and repair.
Fats:
these provide a source of energy and contain fat soluble vitamins.
Vitamins:
these are required in very small quantities to keep you healthy.
Mineral Salts: these are required for healthy teeth, bones, muscles etc..
Fibre: this is required to help your intestines function correctly; it is not
digested.
Balanced Diets: we must have the above items in the correct proportions.
Carbohydrates
Carbohydrates are the most important source
of energy. They contain the elements Carbon, Hydrogen and Oxygen. The first part
of the name "carbo-" means that they contain Carbon. The second part of the name
"-hydr-" means that they contain Hydrogen. The third part of the name
"-ate-" means that they contain Oxygen. In all carbohydrates the ratio of
Hydrogen atoms to Oxygen atoms is 2:1 just like water.
We obtain most of our carbohydrate in the form of starch.
This is found in potato, rice, spaghetti, yams, bread and cereals. Our digestive system
turns all this starch into another carbohydrate called glucose. Glucose
is carried around the body in the blood and is used by our tissues as a source of energy.
(See my pages on respiration and balanced
chemical equations.) Any glucose in our food is absorbed without the need for
digestion. We also get some of our carbohydrate in the form of sucrose;
this is the sugar which we put in our tea and coffee (three heaped spoonfuls for me!).
Both sucrose and glucose are sugars, but sucrose molecules are too big to get into the
blood, so the digestive system turns it into glucose.
When we use glucose in tissue respiration we need
Oxygen. This process produces Carbon Dioxide and water and releases energy for other
processes. Now try my starch test
in the Virtual Laboratory
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Proteins
Proteins are required for growth and repair.
Proteins contain Carbon, Hydrogen, Oxygen, Nitrogen and sometimes Sulphur. Proteins are
very large molecules, so they cannot get directly into our blood; they must be turned into
amino-acids by the digestive system. There are over 20 different
amino-acids. Our bodies can turn the amino-acids back into protein. When our cells do this
they have to put the amino-acids together in the correct order. There are many millions of
possible combinations or sequences of amino-acids; it is our DNA which contains the
information about how to make proteins. Our cells get their amino-acids from the blood.
Now try my Biuret test in
the Virtual Laboratory
Proteins can also be used as a source of energy.
When excess amino-acids are removed from the body the Nitrogen is excreted as a chemical
called urea. The liver makes urea and the kidney puts the urea into our
urine.
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Fats
Like carbohydrates, fats contain the elements
Carbon, Hydrogen and Oxygen. Fats are used as a source of energy: they are also stored
beneath the skin helping to insulate us against the cold. Do not think that by avoiding
fat in your diet you will stay thin and elegant! If you eat too much carbohydrate and
protein, you will convert some of it into fat, so you will put on weight. You must balance
the amount of energy containing foods with the amount of energy that you use when you take
exercise.
You must have some fat in your diet because it
contains fat soluble vitamins.
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Vitamins
Vitamins are only required in very small
quantities. There is no chemical similarity between these chemicals; the
similarity between them is entirely biological.
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Vitamin A: good for your eyes.
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Vitamin B: about 12 different chemicals.
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Vitamin C: needed for your body to repair itself.
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Vitamin D: can be made in your skin, needed for
absorption of Calcium.
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Vitamin E: the nice one - reproduction?
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Mineral Salts
These are also needed in small quantities, but we
need more of these than we need of vitamins.
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Iron: required to make haemoglobin.
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Calcium: required for healthy teeth, bones and
muscles.
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Sodium: all cells need this, especially nerve
cells.
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Iodine: used to make a hormone called thyroxin.
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Fibre
We do not // can not digest cellulose.
This is a carbohydrate used by plants to make their cell walls. It is also called
roughage. If you do not eat foods materials which contain fibre you might end up with
problems of the colon and rectum. The muscles of you digestive system mix food with the
digestive juices and push food along the intestines by peristalsis; if there is no fibre
in your diet these movements cannot work properly.
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A Balanced Diet
You must have carbohydrate, protein, fat,
vitamins, minerals salts and fibre in the correct proportions. If there is not enough
protein, you will not be able to grow properly and you will not be able to repair yourself
i.e. wounds will not heal properly. If you do not have enough energy containing foods you
will feel very tired, you will not have enough energy. If you have too much energy
containing foods you will become overweight. If you think that you are overweight you
might try taking more exercise to "burn off" some of the excess food which you
ate at you last meal.
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